Distributions of potassium, sodium, calcium phosphorus and sulphur were obtained from dried cryosections of rapidly frozen synaptosomes and cerebellum. The synaptosomes derived from cholinergic endings of squid optic lobe were imaged by emission of characteristic x-rays with the use of an energy dispersive spectrometer. Specimens were cooled to -120 C in a special cryotransfer sample stage, in order to minimize mass loss by radiation damage. The digitally acquired elemental maps showed a bimodal distribution of potassium and sulphur in the synaptosome population. This result suggests that only a fraction of synaptosomes with high potassium and low sodium are physiologically equivalent to the cholinergic endings of in vivo cells. In an effort to understand changes in potassium and calcium concentrations that occur in cerebellum trauma, rat cerebellum cryosections were analyzed. Although little contrast, apart from compression artifacts, was visible in the elastic images, potassium maps obtained at a resolution of some 50 nm revealed areas of differing K concentration (60 - 180 mmol). These regions may correspond to dendrites, axons and glial cells. Regions containing calcium were found with concentrations in the range 20-50mmol, and these may correspond to organelles involved in calcium regulation.